Conventionally, a typical baseband circuit in a receiver includes a variable gain amplifier (VGA) and an analog-to-digital converter (ADC). A VGA is used as a gain controller which adjusts an amplitude of a baseband signal to fall within a predetermined range (specifically, an input range of an ADC) by controlling a gain to be supplied to the baseband signal. An ADC converts a baseband signal in which the amplitude is adjusted by the VGA into a digital signal.
There is a baseband circuit structure to suppress power consumption of an ADC. The ADC generates an oscillation signal having a frequency controlled by a voltage value of a baseband signal, and generates a digital signal by performing frequency-to-digital conversion of the oscillation signal. However, in this procedure, a baseband signal in which the amplitude has been adjusted by a VGA is used.
However, power consumption of the VGA can be a problem for the baseband circuit. In addition, noise of the VGA is also added to the baseband signal.